1. Field of Invention
The present invention relates to a semiconductor technology, and more particularly, to a method for manufacturing gallium nitride based light emitting diodes of a back hole structure.
2. Description of Prior Art
As the breakthrough of the third generation semiconductor materials, gallium nitride, and the birth of blue, green and white light emitting diodes, a new industry revolution, an illumination revolution, is being gestated following the microelectronics revolution induced by the semiconductor technology, and the indication thereof is that semiconductor lamps will gradually replace incandescent lamps and fluorescent lamps. Semiconductor lamps use light emitting diodes (LEDs) as new light sources, and with same brightness, the power consumption of the semiconductor lamps is only 1/10 of that of normal incandescent lamps, but the lifetime is extended by 100 times. Semiconductor illumination (also referred as solid state illumination) has wide range of applications in large screen displaying, traffic signal lamps and general-purpose or special-purpose illumination fields due to the advantages of power saving, long lifetime, free of maintenance, and environmental protection. As is generally considered, the tendency of the semiconductor lamps to take place of conventional incandescent lamps and fluorescent lamps is certain, just as the transistors take place of the electronic tubes. The three magnates of the world illumination industry, GE, Philips and Osram, have cooperated with semiconductor corporations and established semiconductor illumination enterprises, and proposed to increase the emitting efficiency of semiconductor lamps by 8 times more and decrease the price by 100 times. A war to occupy the apex of new semiconductor illumination industry has broken out all over the world. US Department of Energy predicts that semiconductor lamps will replace 55% of incandescent lamps and fluorescent lamps around 2010 and 35 billion dollars can be saved in terms of power. Japan has proposed that conventional incandescent lamps will be widely replaced by semiconductor by 2006. As is forecasted, semiconductor illumination can form a big industry of 50 billion dollars only in US after 7 years.
Compared with conventional structure, a flip-chip structure can increase light output, enhance luminous intensity, improve heat dissipation, and increase operating current. The method generally used at present for manufacturing gallium nitride based LEDs using the flip-chip bonding technique is depositing insulation silicon oxide with poor heat conductivity on a silicon chip, forming metal electrodes on the silicon oxide, plating bumps and being flip-chip bonded with the die. In such structure, heat produced in the active region passes through the silicon oxide, which is a poor heat conductor, then is conducted to a heat sink through the silicon chip, and finally attached directly to the heat sink by the heat conduction glue. Although this method can partly solve the problem of heat dissipation, the thermal resistance is yet large enough to preventing a high power type LEDs from being used in the general-purpose illumination in the future.